There is an issue running this demo on Windows and Linux; it will not run without drag 'n dropping all seven JavaFX module jars onto the open sketch window. See this thread: Processing and JavaFX
I have the same problem on Windows 11 and Linux even though I installed the JavaFX library and a javafx folder is in the libraries folder where it’s supposed to be. I drag 'n dropped the seven jar files onto the open sketch window in the editor and that fixed it; copy/paste of the jar files into the sketch folder did not work. Processing adds the modules to a folder named ‘code’ after a drag 'n drop. The demo above runs ok on MacOS so it appears to be a Windows and Linux issue. Before the pull request to add all seven JavaFX modules to the editor source code was approved, one of the reviewers tested it on Windows and reported no problem so I’m not sure where the problem lies. If others have trouble I guess we will need to file a ‘bug’ report; we shouldn’t have to drag 'n drop the jar files every time we want to run a JavaFX demo in Windows or Linux.